Inkjet printers form printed images using one or more printheads that include arrays of inkjets ejectors. A controller in the printer operates the inkjets to form printed images that often include both text and graphics and may be formed using one or more ink colors. Some printer embodiments employ multiple printheads that each includes hundreds or thousands of ejectors. Multiple printheads form different portions of a printed image and, in multicolor printer configurations, different printheads emit different ink colors to form multicolor printed images.
During operation, some printer embodiments monitor the alignment and operation of the printheads that form printed images. Two printheads are “registered” with each other when the printheads are aligned with each other in a predetermined configuration to enable ink drops ejected from both printheads to land on appropriate regions of an image receiving surface to form printed images. For example, two printheads that eject different colors of ink may be aligned with each other in a cross-process direction to enable both printheads to print ink onto the same region of a print medium. The two printheads eject drops that appear to blend together to form all or portions of multicolor images on the print medium. In another configuration, an array of two or more printheads are registered across the print zone in a “stitched” configuration that enables two or more printheads to form continuous printed images that are wider than the width of an individual printhead.
To maintain registration between printheads, the printer operates the printheads to form a predetermined arrangement of printed marks that is referred to as a “test pattern.” An optical sensor scans the printed test patterns to enable a controller or other image processing device to identify the individual marks. The controller identifies misregistration between printheads and optionally identifies inoperable inkjets in the printheads based on the positions of the printed marks in the test pattern. Prior art test patterns include regular arrays of printed dashes where a single inkjet ejects a series of ink drops to form a continuous dash in the test pattern.
One drawback of prior art test patterns is that the analysis of scanned image data for printhead registration and inoperable inkjet detection becomes less reliable when multiple marks near the edges of the test pattern are missing. In some instances, the edges of a paper print medium curl and make contact with some of the inkjets near the edges of the print zone. The paper absorbs ink from the inkjets and produces a temporary malfunction of the inkjets near the edges of the print zone. Printed test patterns that do not include a comparatively large number of marks at the edges of the test pattern may provide inaccurate information during printhead registration and inoperable inkjet detection processes. Consequently, improved systems and methods for the generation and analysis of printed test patterns that remain effective for printed test patterns that are formed with missing marks would be beneficial.